Chemical doping is an important strategy to alter the charge transport properties of both molecular and polymeric organic semiconductors, and finds application in organic electronic devices, for instance in organic light-emitting devices (OLEDs). Various materials have been reported for their use as p-dopants, for example, ranging from strongly electron-accepting organic molecules such as 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4-TCNQ) to transition metal oxides such as WO3 (Meyer, J. et al., Mater. Chem. 2009, 19, 702), metal organic complexes such as molybdenum tris-[1,2-bis(trifluoromethyl)ethane-1,2-dithiolene] (Qi, Y. et al., J. Am. Chem. Soc. 2009, 131, 12530-12531) and redox active salts such as NOBF4 (Snaith, H. J. et al., Appl. Phys. Lett. 2006, 89, 262114) or (p-BrC6H4)3NSbCl6 (Bach, U. et al., Nature 1998, 395, 583-585. Many of these materials are usually applied by vacuum deposition techniques and exhibit low solubility in organic solvent, others are facing stability issues or are reactive and prone to side reactions.
It is thus an objective of the present invention to provide a new class of dopants that allows to easily tune the chemical, physical, optical and/or electronic properties of the doping agent in order to carefully adapt it to the desired application. For example, for OLEDs, doping of interfaces might be preferable, which is easier if the dopant is deposited by thermal evaporation. Dopants based on metal complex having negatively charged ligands, for example, may be used to obtain neutral complexes that can be deposited by thermal evaporation. Doping at interfaces by evaporation could be used for OLEDs, organic solar cells and also the solid state dye-sensitized solar cells (ssDCSs).
Furthermore, it is an objective to provide dopants the solubility of which can be adjusted. For example, it is an objective to provide dopants that are easily soluble in organic solvents, that are stable and that do not engage in undesired side reactions in the device. Besides the solubility, the dopants are ideally charged or neutral to use by thermal evaporation in organic light emitting diodes, and solar cells.
In organic light emitting diodes (OLED), one problem of dopants is their diffusion across the different layers of the OLED, leading to a reduction in performance or even loss of function. It would thus be advantageous to provide dopants the diffusion of which can be controlled, for example by using suitable counter ions.
Dopants are also used in solid state (ss) dye-sensitized solar cell (DSC) applications, in which the liquid electrolyte is replaced by a solid hole transporting material (HTM). In particular when using 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)-9,9′-spirobifluorene (spiro-MeOTAD) as HTM, high power conversion efficiencies have been yielded. Bach et al. (1998) were the first to report on the use of spiro-MeOTAD in ssDSCs and although research interest to identify competitive alternatives is strong, spiro-MeOTAD is still the system of choice when high efficiencies are demanded. Several intrinsic properties like its glass transition temperature, solubility, ionization potential, absorption spectrum and solid-state morphology make Spiro-MeOTAD a suitable candidate for DSC applications. However, similar to other organic hole conductors including liquid hole conductors, spiro-MeOTAD suffers from a relatively low conductivity in its pristine form. It is an objective to provide dopants that can also be used in liquid organic charge transporting materials.
It is an objective of the invention to provide means for increasing conductivity of charge transporting materials, in particular of hole and/or electron transporting materials, such as, for example, organic conductors or semiconductors.
It is also an objective of the invention to provide a means to improve charge collection and/or charge transfer, for example at the interface, in particular in case dopants are applied by evaporating the dopant.
With respect to solid state dye-sensitized solar cells (ssDSCs) it is noted that Bach et al (1998) already employed (p-BrC6H4)3NSbCl6 as a chemical p-dopant but up to the present date, no detailed study on p-type doping in dye solar cells has been reported. Surprisingly, the use of chemically p-doped spiro-MeOTAD has gradually diminished and most of the recent publications on spiro-MeOTAD-based ssDSCs do not follow this strategy. The reason, why high power conversion efficiencies can still be achieved, is the device fabrication under atmospheric conditions and a facile reaction of spiro-MeOTAD with molecular oxygen under illumination, a process referred to as photo-doping. Therefore, it is currently believed that chemical p-doping is not necessarily the key to high performance. On the other hand, photo-doping is clearly a process that is not easy to control. Therefore, it is an objective of the present invention to provide means of increasing conductivity of organic charge transporting materials by other and/or additional ways than by photo doping. It is in particular an objective to increasing conductivity of organic charge transporting material in a highly reproducible way and to fabricate stable electrochemical devices using organic charge transporting materials.
With respect to rechargeable batteries, such batteries are used in many electronic devices, in particular portable devices, such as cell phones, laptops, tablet computers (iPad, etc), portable computer game consoles and so forth, for example. Rechargeable batteries, in particular lithium-ion batteries, may experience thermal runaway resulting in overheating. Sealed cells will sometimes explode violently. Lithium-ion batteries can rupture, ignite or explode when exposed to high temperature. For example, short-circuiting may cause the cell to overheat and possibly catch fire. It is an objective of the invention to provide ways for preventing or reducing the risk of explosion and/or the risk of over-discharging.
It is also an objective of the invention to provide agents that can be used for protecting electronic devices, in particular electrochemical devices against overvoltage.
The present invention addresses the problems and objectives depicted above, which are part of the present invention.